US 7839844 B2
A packetized data transmitter notes packet transmission times and the times, if any, of retransmission requests from a receiver. Based on the period between original transmission and retransmission of a dropped packet, the transmitter establishes a packet discard period, essentially a transmitter packet buffer length.
1. A packetized data transmitter dynamically establishing, for each packetized data stream during transmission of the stream, a packet expiration period to be used for determining whether previously transmitted packets should be discarded from a retransmission queue at the transmitter by flushing the queue, wherein the transmitter determines whether it has received a request from a receiver to retransmit a packet and if so, retransmits the requested packet and revises the packet expiration period at least in part by determining a difference between a time the packet as identified by its packet ID was first transmitted to the receiver, and a time the packet of the same packet ID is retransmitted, and/or by determining a difference between a time the packet was first transmitted, and a time the request to retransmit is received by the transmitter.
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7. A packetized data transmitter, comprising:
a processor executing logic including:
receiving, from a receiver at a request time, a request for retransmission of a packet transmitted at an original transmission time;
retransmitting the packet in response to the request;
in response to the request, determining a packet expiration period at least in part by measuring a period from the original transmission time of the packet to at least one time in the group of times consisting of: the request time, and a time of retransmitting the packet; and
using the packet expiration period to determine whether to discard packets from retransmission buffer in the transmitter by flushing the packets from the buffer.
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This application is a continuation-in-part of and claims priority from co-pending U.S. patent application Ser. No. 10/903,171, filed Jul. 30, 2004.
The present invention relates generally to packetized data communication systems.
When transmitting data from a server to a computer system, or from a computer system to another computer system, it is not guaranteed that 100% of the data requested by the user will arrive. Often times some of the data is lost in the transmission or is never sent at all.
Accordingly, methods have been provided for verifying proper receipt of data and when, for instance, a packet in a packetized data stream is not received, for requesting retransmission. In these methods, a data verification layer in a communication protocol stack tracks the received packets and requests retransmission if a packet does not arrive as expected.
As recognized herein, current standards for tracking data often contain overhead and latency which is too high for certain data streaming environments, such as telephony. Nonetheless, a receiver must buffer data before sending it on to higher levels in the protocol stack while waiting for a retransmitted packet. Likewise, after sending data a transmitter must buffer it for a period after transmission, in case the receiver requests retransmission. The length of the transmitter buffer (sometimes referred to as a discard period) in current systems is predefined in an attempt to balance the need to wait long enough for a dropped packet to be requested and retransmitted, but to also avoid having to accumulate more packets post-transmission than is necessary. In terms of the transmitter buffer, a buffer length that is too long requires more memory than is necessary, while a buffer length that is too short means that the retransmission mechanism will not function. The present system is presented in response to the above critical observations.
A method for establishing a packet buffer length in a packetized data delivery system includes, upon initially receiving a packetized data stream, requesting retransmission of a received packet. The method also includes receiving a retransmitted copy of the packet. Based at least in part on the requesting and receiving acts, the buffer length is established.
If desired, an ID of the packet for which retransmission is requested and a time of retransmission request are recorded. Also, a time of receipt of the retransmitted copy is recorded, with the method then using the difference between the time of receipt of the retransmitted copy and the time of retransmission request to establish the buffer length. Preferably, the requesting, receiving, and establishing acts are executed substantially at the beginning of each new packetized data stream being transmitted. The buffer length may be used to delay sending packets to higher communication protocol levels in the event of a missed packet.
In another aspect, a packetized data receiver includes a receiver system that establishes a lower level in a packetized data communication protocol stack. The receiver system requests a retransmission of a received packet at or near the beginning of a packetized data stream being received by the receiver. The logic of the receiver system determines a time period measured from the time of requesting a retransmission until receipt of a retransmitted packet that correlates to the received packet. A buffer delay period is then established based on the time period. The buffer delay period is used in the event of a missing packet to buffer data before sending it to higher levels in the protocol stack.
In yet another aspect, a packetized data receiver establishes, for each packetized data stream received and substantially at the beginning of receiving each respective stream, a time delay to be used in the event that a packet is missed for sending packets to higher levels of a protocol stack.
In a transmitter embodiment, a method for establishing a packet discard period includes, upon initially transmitting at least one packet in a packetized data stream, recording a time of transmission of the packet. The method also includes receiving a request for a retransmitted copy of the packet, and retransmitting the packet. Based at least in part on the recording and retransmitting acts, the packet discard period is established.
In some embodiments a difference is used between the time of transmission and a time of retransmission to establish the packet discard period. The discard period can be executed substantially only at the beginning of each new packetized data stream being transmitted, or it can be executed for all retransmitted packets in a packetized data stream, or it can be executed periodically for some but not all retransmitted packets in a packetized data stream. The packetized data may be in user datagram protocol (UDP).
In another aspect, a packetized data transmitter executes logic that includes receiving, from a receiver at a request time, a request for retransmission of a packet that had already been transmitted at an original transmission time. The logic also includes determining a packet expiration period measured from the original transmission time to the request time and/or to a time of retransmitting the packet. Using the packet expiration period, it is determined whether to discard packets from a retransmission buffer in the transmitter.
In yet another aspect, a packetized data transmitter establishes, for each packetized data stream transmitted and substantially at the beginning of transmitting each respective stream, a packet expiration period to be used for determining whether previously transmitted packets should be discarded from a retransmission queue at the transmitter.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:
Referring initially to
With the above in mind, the exemplary receiver 12 includes a processor 16 that can access a program storage device 18 to execute the logic shown below in
Now referring to
Proceeding to decision diamond 66, it is determined whether the retransmit action has failed as indicated by an excessive period elapsing without receiving the retransmitted packet from the transmitter. If it has, the logic reverts back to block 62 and starts over again. If the action has not failed, a packet has been received and the logic proceeds to block 68.
Still referring to
Should it be determined at decision diamond 70 that the packet received at block 68 is not the next one in sequence, the logic flows from decision diamond 70 to decision diamond 74, wherein it is determined, by means of comparing the ID of the packet received at block 68 with the packet ID recorded at block 64, whether the packet received was the test packet. If the logic determines that it was the test packet, the logic proceeds to block 76 wherein the time period between the time recorded at block 64 and the time the test packet was received at block 68 is determined. Because this period can be correlated to a buffer length by, e.g., multiplying the data rate by the measured retransmission delay period to find a total number of data elements that must be buffered during the retransmission delay period determined at block 76, the length of the buffer 20 shown in
Returning to decision diamond 74, if the packet received at block 68 is not the test packet, the logic proceeds to decision diamond 80, wherein it is determined whether the packet is a retransmitted packet from a slot in the packet stream at which a packet was missed. If it was, the logic then flows to block 82 where the packet is inserted into its correct slot in the queue for subsequent passing on to the upper levels of the protocol stack.
In contrast, if, at decision diamond 80, the logic determines that the packet received is not a retransmitted packet but rather some other packet out of sequence, indicating that some packet or packets have been missed, the logic moves to block 84 where a request for the retransmission is made of the missed packet(s) (i.e., those preceding the packet received at block 68 that should have followed the latest packet before that in the buffer). After the request has been made, a space in the data stream for the missed packet is reserved at block 86, and then the logic moves to block 72 to function as set forth above.
Now referring to
The transmitter 112 shown in
Now referring to
Moving to decision diamond 140, the transmitter 112 determines whether it has received a request from the receiver 114 to retransmit a packet. If not, the logic proceeds to decision diamond 142 to determine whether any packets in the discard queue have expired by, e.g., comparing their times of transmission with the below-established expiration period. In the first iteration (i.e., for the first packet) the test at decision diamond 142 should be negative, in which case the logic loops back to block 134 as shown to retrieve the next packet in the stream for transmission. In the event that expired packets exists in the discard queue at decision diamond 142, the packet(s) are discarded, e.g., flushed from the buffer 120, at block 144.
In the event that a retransmission request is received by the transmitter 112 at decision diamond 140,
Block 150 indicates that the transmitter buffer length, i.e., the packet expiration period used at decision diamond 142, may be adjusted using the calculation at block 150. The adjustment may include simply resetting the expiration period to the period most recently obtained at block 150, or it may include averaging the period obtained at block 150 with previous periods such that the expiration period used at decision diamond 142 represents an average of measured retransmission periods. If desired, the steps at blocks 148 and 150 may be performed only once, e.g., for the first packet transmitted in a stream, or they may be performed for each retransmitted packet as shown, or for only some packets on a periodic basis. In any case, the amount of data kept in the buffer 120 is dynamically established for each stream transmitted.
While the particular SYSTEM AND METHOD FOR DYNAMICALLY DETERMINING RETRANSMIT BUFFER TIME as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. It is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. Absent express definitions herein, claim terms are to be given all ordinary and accustomed meanings that are not irreconcilable with the present specification and file history.